Electric spark igniter with improved cooling structure



Dec. 6, 1960 c, J, MATTERS 1 2,963,602

ELECTRIC SPARK IGNITER' WITHIMPROVED COOLING STRUCTURE Filed July 7, 1954 In vent-or:

Clarence J Watt-era, I

H/ls Attorney.

United stateg tent ELECTRIC SPARK IGNITER WITH IMPROVED COOLING STRUCTURE Clarence J. Watters, Schenectady, N.Y., assignor to General Electric Company, a corporation of New York Filed July 7, 1954, set. No. 441,729 4-Claims. or. 313-115) for the cooling thereof, and more particularly to such a structure which is especially adapted for use in fuel combustion apparatus of the type having a continuous flow of combustion materials therethrough. p

It is a commonly recognized problem in combustion apparatus of the continuous flow type such as combustion gas turbines, for instance, in which there is a continuous flow of combustible materials burning at very high temperatures, that care must be taken in the selection of materials and components to prevent high rates of deterioration and destruction due to the continuous exposure to high temperature. This problem has been recognized in particular with relation to electric spark igniters or spark plugs which must be employed to initiate combustion. One present igniter structure dealing with this problem includes an insulator member surrounding and supporting a center electrode and an outer casing member serving as a second electrode which surrounds the insulator member in spaced relation therewith. Cooling air is provided within the space in the casing and surrounding the insulating member so that such cooling air flows past the insulating member through this space and into the combustion space of the combustion apparatus. One example of such a structure is shown, for instance, in copending patent application Serial Number 382,269, filed on September 25, 1953, by Donald C. Peroutky for a Fuel Combustion Ignition Device and assigned to the same assignee as the present application. It is apparent from the above description that in these structures the cooling air passes between the end of the casing of the igniter which serves :as the outer electrode and the insulating member. The cooling air thus passes between the electrodes and thus through the path traversed by the spark discharge between the electrodes. This continuous flow of cooling air tends to impede the initiation of the spark discharge and causes a continuous cooling of the spark as it is projected into the discharge area. The effectiveness of the spark for initiating combustion of the combustible materials is thus seriously impaired.

Accordingly, it is one important object of this invention to provide an improved electric spark igniter in which the spark itself is not cooled by the igniter cooling fluid.

Another object of this invention is to provide an improved electric spark igniter structure which is cooled by a flow of cooling fluid in which the cooling fluid is not discharged into the spark discharge area.

Another problem with the structure as described above is that the cooling fluid or air expelled from the igniter in the spark discharge area tends to thin the combustible material, creating a higher proportion of air to fuel and making a mixture which is too lean for the proper and expeditious initiation of combustion.

Accordingly, it is another object of the present invention to provide an improved air cooled electric spark -igniter in which the cooling air is not discharged in .such

2,963,602 Patented Dec. 6, 1960 a location as to thin the combustible mixture in the spark discharge area.

As is pointed out in my copending patent application Serial No. 441,730 for a Spark Projection Ignition Device, filed on even date herewith and assigned to the assignee of the instant application, now U.S. Patent No. 2,840,742, issued June 24, 1958, it has been found that the operation of such a device is greatly improved by the provision of a semi-conductive surface on the insulating member in the area extending between the two electrodes. In order to obtain the maximum benefit of such a semi-conductive insulator surface in lowering the voltage required to initiate the spark discharge, it has been found desirable to establish an electrical connection between both electrodes and the semi-conductive surface. It has been found desirable therefore to seal the sparking end of the casing to the insulator surface in order to obtain a good electrical connection therebetween. It is diflicult in such an improved structure to provide for the discharge of cooling fluid'between the insulator and the outer electrode formed by the end of the casing.

Accordingly, it is another important object of this invention to provide an improved fluid cooled electric spark igniter employing an insulating member having a semiconductive surface in which the outer electrode is sealed and electrically connected to the semi-conductive surface and in which the electrical connection is unimpaired by cooling fluid discharge openings.

Another problem which has been encountered is that the igniter, as it protrudes into the combustion space, interferes with the smooth and continuous flow of the combustible mixture, causing improper combustion and undue accumulations of solid carbon materials. This feature has also been known to result in the operation of this protruding part as a flameholder which tends to create a turbulent area of a lesser velocity in the burning materials which therefore burn more extensively in this location, imparting a greater destructive heating effect to the surrounding parts, including the igniter structure itself. 4

Accordingly, it is another important object of this invention to provide an improved electric spark igniter of the air-cooled type which does not interfere with the smooth flow of combustion materials and which does not act as a flameholder.

It is another object of the invention to provide an improved fluid cooled electric spark igniter structure especially adapted for operation in apparatus having a continuous flowof combustible materials in which the continuous flow of combustible materials assists in inducing the flow of the igniter cooling fluid.

Other objects and advantages of this invention will be apparent from the following specification and the accompanying drawings.

In carrying out the above objects of this invention in one form an electric spark discharge igniter structure may be employed having an insulating member supporting a center electrode with a casing member forming an outer electrode surrounding the insulating member and fitted thereto at the sparking tip. An annular space is provided between the casing member and the insulating member for the passage of cooling air and openings are provided in the side walls of the casing member to admit and discharge the cooling air. The air inlet opening is preferably arranged and oriented to intercept a flow of cooling air exterior to the combustion chamber served by the igniter and the air discharge openings are disposed adjacent to the sparking tip on the downstream side of the igniter structure with respect to the normal direction of flow of combustible materials. For a better understanding of the invention, reference should be made to 3 the following specification and the accompanying drawing in which:

Fig. 1 is a sectional side view of one preferred embodiment of the igniter structure of this invention;

Fig. 2 is a sectional bottom end view through the section 2-2 of the device of Fig. 1; and

Fig. 3 is a partial sectional view of a fuel combustion chamber of the type in which the igniter of this invention may be employed showing the igniter of Fig. 1 installed therein. 1

Referring more particularly to Fig. 1, there is shown a sectional view of an igniter constructed in accordance with this invention and designated as a whole as 10. This structure includes an outer casing or shell 11 within which there is supported an insulating member 12. The insulating member 12 has a smaller diameter over most of its length than the inside diameter of the casing 11 so as to provide a cooling air passage 13 therebetween. Cooling air is supplied to the passage 13 through an air inlet opening in the side of the casing 11 at 14. The cooling air follows paths within the space 13 such as illustrated by the section line 2-2 and is discharged through a series of air discharge openings 15 provided in casing 11 at a position axially displaced from 14. The relationships of the inlet and discharge openings 14 and 15 are also clearly shown in Fig. 2, which is a sectional bottom end View of the structure of Fig. 1 taken at the section 2-2.

Referring again to Fig. 1 in more detail, the lower end of the insulating member 12 is seen to have a reduced diameter portion at the bottom thereof in the drawing to thus form a shoulder. The casing member 11 includes an inwardly extending flange 16 at the lower end thereof which provides a reduced lower opening in which a metallic bushing 16a is supported. This bushing is preferably composed of a spark erosion resistant material such as metallic nickel. Within the bushing 16a, the insulating member 12 is supported. Supported within the insulating member, in the central bore thereof, there is a center electrode 17.

The lower end of the center electrode terminates substantially above the lower (firing) end of the insulating member 12. This is a feature which constitutes a portion of the material described and claimed in the above-mentioned copending patent application, Serial No. 382,269 of Donald C. Peroutky.

It is preferred that the surface of the insulating member 12, at least in the portions which are in engagement with the center electrode 17 and the casing flange 16 forming the outer electrode and extending between these electrodes, should be comprised of a semi-conductive material. It has been found that the employment of a semi-conductive insulator surface between electrodes provides for the initiation of the spark discharge at a lower initiation voltage. The combination of a semi-conductive insulator surface in an igniter structure incorporating a recessed center electrode as shown and described here constitutes a portion of the material described and claimed in my aforementioned copending patent application Serial No. 441,730, now US. Patent No. 2,840,742, issued June 24, 1958. The semi-conductive surface is indicated at 18. The lower flange portion 16 of the easing member 11 is in closely fitting mechanical engagement with the bushing member 16a. It will be understood that this mechanical engagement also establishes an electrically conductive contact between the flange 16 and the bushing 16a.

Because of this electrical interconnection, the bushing 16a may be considered as effectively an integral part of the outer electrode formed by the flange 16 and the easing 11. Accordingly, where the casing 11 or the flange 16 or the outer electrode are referred to without separate reference to the bushing member 16a, these terms will be ing 16a is preferably sealed around the periphery of the lower shoulder of the insulating member 12 to the semiconductive surface by means of a high temperature brazing material such as silver solder. A similar mechanical and electrical connection is preferably established between the semi-conductive surface of the insulator 12 and the center electrode 17 and this connection may be made more secure by the provision of a groove in the surface of electrode 17 such as shown at 19. The lower end of the igniter including the flange portion 16 and the structure surrounded thereby may be referred to below as the sparking tip or the firing end, and the end area of this lower end in Fig. 1, as the spark discharge area.

At the upper end of the igniter structure as shown in Fig. 1, the outer portion of the insulating member 12 is enlarged as indicated at 20 to a diameter slightly smaller than the inner bore diameter of the casing member 11 so as to provide a sliding fit therein. This portion of the insulating member 12 is preferably sealed around its entire periphery to the adjacent inner surface of the casing member 11 as shown at 20a. This seal may be made by a suitable brazing material such as silver solder. The insulating member 12 is thus positively positioned within the casing member 11 and the seal at 20a also serves to provide a gas tight closure for the upper end of the cooling air space 13. The inner portion of the insulating member 12 in this upper end 20 is provided with an enlarged opening as indicated at 21 into which the center electrode 17 extends. This structure provides a pin connector by which an electrical connection may be established through a suitable pin socket connector (not shown) to a suitable spark generation apparatus (not shown). An electrical and mechanical connection may also be established between the pin socket connector and the casing member 11 (which also serves as the outer igniter electrode) by means of suitable screw threads as indicated at 22 on the exterior of the upper portion thereof. An igniter mounting flange 23 is also preferably provided which may be positioned against a suitable integral flange 24 on the exterior of the casing 11 and brazed or welded thereto.

As mentioned above, Fig. 2 is a bottom end view through section 2-2 of the igniter structure shown in Fig. 1. This figure clearly shows the path which is provided for the cooling air through the inlet opening 14, the passage 13, and the discharge openings .15. As shown in this Figure 2, the mounting flange 23 may include two mounting holes 23a which are slightly offset from the center line of the casing 11. When suitable mounting holes are provided in the combustion apparatus, it is therefore impossible to assemble and mount the igniter device without the proper alignment.

In Fig. 3 there is shown a partial sectional view of a combustion chamber, designated as a whole as 25, of the type in which the igniter structure 10 of this invention is intended to be employed. This combustion chamber may preferably be constructed in accordance with the teachings of Patent 2,601,000, issued June 17, 1952 to A. J. Nerad and assigned to the same assignee as the present invention. The structure surrounding the chamber includes an outer shell 26 and an inner shell 27 within which there is a suitable fuel nozzle 28. This combustion apparatus is of the continuous fiow type such as is employed in fuel burning gas turbines. The combustion air, under pressure, is supplied between the chamber walls 26 and 27, as indicated by the arrow 29, from a suitable source such as an engine driven compressor. This compressed air which flows between the walls 26 and 27 provides a source of cooling fluid for the igniter 10. Igniter 10 is here shown in slightly enlarged proportions with respect to the remainder of the chamber structure 25. The igniter is attached and mounted to the outer combustion chamber wall 26 and extends through a suitable opening in the outer wall 26 and a second opening in the inner chamber wall 27.

A portion of the air which is flowing between the walls 26 and 27 enters the igniter cooling air inlet opening 14, as indicated by the arrow at 30, and is discharged through the discharge openings 15 as indicated by the arrow at 31. The inlet opening 14 in the igniter is aligned in the direction of the flow of cooling air between the walls 26 and 27, and pointed upstream with respect to that flow. It will also be seen that the discharge openings in the casing 11 of the igniter 10 are directed downstream with respect to the flow of fuel which is directed from the fuel nozzle 28 and the flow of associated combustion air enter: ing the inner chamber upstream from the igniter such as at 32.

'It will be seen from the above description and the drawings that the cooling air is not expelled from the openings 15 in the spark discharge area and therefore does not interfere in any way with the spark discharge which occurs at the igniter tip. The cooling air therefore does not cool and extinguish and render the spark less effective nor does it thin the combustible mixture of fuel and air, in the vicinity of the spark at the sparking tip of the igniter. Further, the electrical contact between the electrodes and the semiconductive surface of the insulating member is not interrupted or impaired in any way by the presence of cooling air discharge openings at the immediate vicinity of these connections.

It will also be apparent, particularly by reference to Fig. 3, and the explanation and description accompanying that figure, that the discharge of air from the openings 15 contributes to the continuity in the flow of gases and combustion materials in the vicinity of the igniter structure and helps to prevent an area of turbulence and partial stagnation in the flow of gases in the shadow of the igniter on the downstream side thereof. With the discharge openings 15 on the downstream side of the igniter with respect to the flowof gases within the combustion chamber, the slightly lower pressure which would otherwise exist in the shadow of the igniter is avoided. Thus, the igniter does not and cannot act as a flameholder and accelerated deterioration of the igniter and the formation of undesired carbon deposits are thereby avoided.

While only certain preferred embodiments of the invention have been described and illustrated by way of example in the foregoing, many modifications will occur to those skilled in the art and it therefore should be understood that the appended claims are intended to cover all such modifications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An air cooled electric spark igniter comprising an inner electrode, a tubular outer electrode and a tubular insulating member disposed between said inner and outer electrodes with said electrodes and said insulating member terminating in a sparking tip defining a spark discharge area in which the spark passes between said inner and outer electrodes across the intervening surface of said insulating member, said inner and outer electrodes being circumferentially sealed to said tubular insulating member adjacent said spark discharge area and said outer electrode being spaced from said insulating member in portions thereof removed from said spark discharge area to provide a generally annular cooling air space between said insulating member and outer electrode, said outer electrode including at least one cooling air discharge opening adjacent to but directed away from said spark discharge area and at least one cooling air inlet opening at a position more distantly removed from said spark discharge area than said air discharge opening.

2. An air cooled electric spark igniter comprising an inner electrode, a tubular outer electrode and a tubular insulating member disposed between said inner and outer electrodes with said electrodes and said insulating member terminating in sparking tip portions together defining a spark discharge area in which the spark passes between said inner and outer electrodes across a surface of the sparking tip portion of said insulating member, said insulating member sparking tip surface being of semiconductive material, said inner and outer electrodes each having substantially continuous mechanically sealed electrical connection to said semiconductive surface of said insulating member and said outer electrode being spaced from said insulating member in portions thereof removed from said spark discharge area to provide a generally annular cooling air space between said insulating member and outer electrode, said outer electrode including at least one cooling air discharge opening adjacent to but directed away from said spark discharge area and at least one cooling air inlet opening remote from said spark discharge area.

3. For use in fuel combustion apparatus of the type including a spaced double walled combustion enclosure adapted for continuous flow of combustion materials in a predetermined direction therein and continuous flow of cooling gas in a predetermined direction between the spaced double walls thereof; an electric spark igniter terminating in a sparking tip and adapted to be mounted to extend through said double walls with said sparking tip projecting into said combustion space, said igniter comprising an inner electrode, a tubular outer electrode and a tubular insulating member disposed between said inner and outer electrodes with said electrodes being circumferentially sealed to said tubular insulating member adjacent said sparking tip and said outer electrode being spaced from said insulating member in portions thereof removed from said sparking tip to provide a generally annular coolant space between said insulating member and outer electrode, said outer electrode including at least one cooling gas inlet opening into said coolant space for communication with the cooling gas flow between said double walls and directed upstream thereof, said outer electrode further including at least one cooling gas discharge opening adjacent to but directed away from said sparking tip and directed downstream of the combustion materials flow.

4. An air cooled electric spark igniter comprising a first electrode of hollow tubular form including an inwardly directed generally annular flange at one end thereof forming an axially facing sparking face having an aperture centrally therethrougn, an insulating member disposed within said first electrode and having an end portion received in said electrode sparking face aperture with substantially continuous mechanically sealed connection to said first electrode adjacent said sparking face, and a second electrode disposed within said insulating member mechanically sealed thereto and having a sparking face spaced from said first electrode sparking face whereby the spark traverses the space between said electrodes across the intervening surface of said insulating member end portion, said first electrode being spaced from said insulating member in portions thereof removed from said annular flange to provide a generally annular cooling air space between said insulating member and first electrode, said first electrode including at least one cooling air discharge opening adjacent said annular flange but directed away from said axially facing sparking face and at least one cooling air inlet opening axially spaced from said annular flange.

References Cited in the file of this patent UNITED STATES PATENTS 1,960,344 Muir May 29, 1934 2,013,979 Bray Sept. 10, 1935 2,017,364 Anderson Oct. 15, 1935 2,109,029 Nowosielski Feb. 22, 1938 2,507,278 Smits May 9, 1950 2,625,921 Van Ry Jan. 20, 1953 2,645,082 Sarto July 14, 1953 2,693,082 Arthur Nov. 2, 1954 

